Final answer:
Water is formed when electrons bind to oxygen, the final electron acceptor, at the end of the mitochondrial electron transport chain, which enables ATP production during aerobic respiration.
Step-by-step explanation:
When electrons reach the bottom of the mitochondrial electron transport chain and bind to the final electron acceptor, water (H2O) is formed. Oxygen acts as the final electron acceptor, and upon accepting electrons, it combines with hydrogen ions (protons) to form water. This reaction is crucial for aerobic respiration, allowing the electron transport chain to function and facilitate ATP production, the energy currency of the cell. Electrons are passed through a series of protein complexes and two small diffusible electron carriers, with complex IV being where oxygen is reduced to water, thus maintaining the flow of electrons and the production of ATP.